|Tags to Add
|Tags to Remove
|Not from behind
From the E621 Wiki: Backsack describes when a character's balls are visible from behind. In some cases, is also applied when a character is posed so that the "back" of their balls are visible, but the character is not being viewed from behind. Do not tag if the balls are covered, or otherwise not directly visible.
See the E621 Wiki page on backsack.